This invention relates to an improvement in craft-lifts and more particularly in the means for raising a craft from and lowering a craft into, the water.
The term craft is herein used in its broad generic sense and includes all sports and recreational vessels and boats, powered by engine or sail, in general use. For descriptive purposes, the craft lift is herein described and depicted in use with a typical sport cruiser of average length and width. These are not limitations on or to the invention.
It is well known, and has been ever since craft were invented, that continued exposure to the water ultimately deteriorates the hull of such craft. Salt water may be particularly damaging, but even fresh water storage results in the formation of algae and other deleterious matter on the hull.
The ideal circumstance would be to lift the craft from the water and wash down the hull after and between every use of the craft. In normal use, the craft lies still at the dock in the water more than 90% of its life. Many persons can only use their craft on, for example, weekends, and even at that, not every weekend. The craft merely lies in the water, buffeted by tides and winds, accumulating deleterious material and, in effect, rotting away.
This has been, as stated previously, a known problem since watercraft have existed and many solutions have been devised and offered. Countless systems have been conceived, a continuing tribute to the fact that a problem-free solution has not previously been developed.
It is generally conceded that, for the individual sport or recreational boater, a system which incorporates pontoons or floats, positioned on either side of the craft, is the most preferred and desirable. One of the primary reasons that a floating lifting device is preferred over lifting devices which are required to be fixed in relationship to the bottom structure is that the former will accommodate large variations in water levels without having to allow for these variations in the elevating system, and it is independent of the capacity of the bottom structure to accomodate the load. Such a system is normally anchored to the bottom or fixed in some way to a dock.
In these systems, the framework itself is extended between the floats (a term which will be used herein due to the fact that "pontoon" is somewhat restrictive in definition) and supported thereby. The framework may, but does not necessarily, conform to the general configuration of the hull bottom. Its sole purpose is to support the craft and, accordingly, there is little limitation to its shape and configuration. It may be entirely rigid or portions may be of flexible sheet or web materials. A portion, or all, of the framework is raised or lowered with respect to the plane of the water surface, thereby raising the craft from, or lowering it into, the water.
The above referenced principles within the prior art are such a "given" that they need not to be repeated nor exhaustively described. They are only accoutrements of the system and do not represent inventive structure.
The problem with the prior art systems will become obvious upon a viewing of them vis-a-vis the present invention. All of the prior art structures utilize complex chain, or cable, and pulley systems to lift and lower the craft. There is usually a large wheel or a hand crank for the operator to turn.
Such a system is fine for a healthy, vigorous, strong individual, but not all of those capable of operating the vessel have the strength to turn the crank and lift the vessel. These systems are particularly stressful on elderly individuals or those who may be medically or physically handicapped. If there is no one around to assist these individuals, they must do without and wait for assistance. If in a remote location, such assistance may be long in coming, if at all.
Each of the existing devices have additional characteristics which can adversely affect safety, operational costs, and/or the environment. For example:
Systems using cable-pulley arrangements are subject to failure of any component. Separation of cable or pulley during lifting, lowering, and storage (on those not using a mechanical latch to support the stored boat) can cause serious injury to persons or property. Additionally , since most cable systems utilize a single winch and cable, breakage of a cable can result in catastrophic failure.
The primary disadvantages of evacuated float systems are the time and costs associated with the pumping of the tank, the space occupied by the tanks and the depth of the water required for satisfactory operation. For example, a boat which weighs 3000 pounds requires that 360 gallons of water be pumped each time the boat is raised. At a pumping rate of 20 gallons per minute, raising of the boat takes 18 minutes.
Hydraulic systems utilizing petroleum based, or similar fluids are generally quite expensive and limited to commercial use. In order to reduce the cost of componentry, these systems usually operate at pressures approaching, or exceeding, 2000 psi. Failure of a hose or cylinder can cause serious injury to bystanders. Additionally, the escaping hydraulic fluids, either through catastrophic failure or small leaks, has an adverse effect upon waterfowl, marine organisms, and plant life of the waterways.
They may be manual or motorized, more or less complicated, but all are basically the same system. They are portable, self-contained, capable or suplying a plurality of crafts, on water or land, and are of a relatively low cost.